It is known in the art to provide various security systems for restricting and controlling access to sensitive information stored in electronic equipment.
One such example of prior art is the key apparatus of U.S. Pat. No. 4,298,792. In that system, which is typical of the prior art, the information required to open the lock is contained in a memory, for example a digital PROM located within the machine (see column 3, lines 4-6).
The key system of U.S. Pat. No. 4,200,227 generates a signal which, if recognized by the target system, authorizes access.
A generally similar system is shown in U.S. Pat. No. 4,120,452 in which a memory holder is inserted into the target system but in which the memory holder is primarily an accounting device. Removing the memory holder from the machine does not disable the target machine by removing a portion of the target system memory.